U.S. Pat. Nos. 4,394,481 and 4,419,489 are both incorporated herein by reference. These patents disclose chemically modified asphalt (CMA) which is produced by the long-time reaction, under reflux, of an asphalt, a vinyl aromatic monomer, a rubbery polymer and an acrylamide. Such chemically modified asphalts are disclosed for use as protective coatings for various substrates and are applied, for example, to a cementitious substrate from a solvent carrier, typically a mixture of 80% toluene and 20% normal hexane. U.S. Pat. No. 4,507,365 proposes the use of an environmentally desirable solvent mixture of at least 75% cyclohexane, 15 to 25% toluene, and up to 10% n-hexane for essentially the same CMA.
U.S. Pat. No. 4,456,633 provides a chip seal emulsion of essentially the same CMA in an emulsion which may be cationic, anionic or non-ionic. Such emulsions are intended for use only as an additive for conventional non-chemically modified asphalt emulsions to increase the retention of aggregate, for example, when the combined emulsion is utilized for highway pavement repair. The method of use includes blending the CMA emulsion into the non-CMA emulsion, applying the combination to a pavement, and then applying an aggregate to the applied combination emulsion.
U.S. Pat. No. 4,419,489 discloses essentially the same CMA incorporated into an aqueous emulsion of the cationic rapid set type, the final emulsion comprising 60-65% CMA and 35-40% aqueous medium. The emulsion was intended for use as a cold overlay or as a joint sealer for highways or as a water-resistant membrane. This type of emulsion has been used as a waterproofing basement coating.
The present invention now provides an aqueous emulsion of a mixture or blend of chemically modified asphalt and normal or non-modified asphalt having a penetration ranging from about 10 to about 300, preferably from about 100 to about 300. Especially preferred is a blend of AC-5 asphalt with a CMA prepared by reacting an asphalt, styrene, one or more block copolymers of styrene and butadiene, and an acrylamide, such as dimethylaminopropylmethacrylamide (DMAPMA).
The aqueous emulsion of the present invention is substantially less expensive than the previously utilized CMA emulsion, and has desirable properties for use as a damp-proofing coating for concrete walls, as a primer for adhering asphalt-based membranes to various substrates, such as concrete or wooden surfaces, and the like.
Surprisingly, the outstanding properties of the CMA are largely preserved in the blended non-CMA-CMA coating which results from the application of the emulsion to a substrate and the evaporation of the aqueous emulsification medium. Thus, the unreacted asphalt does not serve merely as a low-cost diluent, since the replacement of from about 5% to about 60% of the CMA with unreacted asphalt does not cause a comparable reduction in the properties of the CMA emulsion. These properties include better low temperature flexibility, higher tensile strength and better elongation characteristics than would have been expected from the dilution of the CMA by the normal asphalt content of the emulsion. Further, the blend of CMA and non-CMA is more easily emulsified than the previous CMA, and the resultant emulsion has better shelf life and is more stable on storage for an extended period of time.